Continuous gage



Nov. 20, 1962 F. sLAMAR CONTINUOUS GAGE 2 Sheets-Sheet l Filed Jan. 7,1960 R R w A y N M W n w S f l w K www M R F PEM kiel .QQ

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Nov. 20, 1962 F. SLAMAR CONTINUOUS GAGE 2 Sheetssheet 2 Filed Jan. 7,1960 /N VE N 0f? FRA/VK SLAMAR Attorney 3,065,415 CONTINUOUS GAGE FrankSlamar, Monroeville, Pa., assignor to United States Steel Corporation, acorporation of New Jersey Filed Jan. '7, 1960, Ser. No. 1,000 8 Claims.(Cl. 324-61) This invention relates to a gage for measuring thethickness of a metal plate between parallel surfaces thereof. t relatesmore particularly to a gage for continuously measuring the thickness ofthe flanges or web of a beam as it travels over a roller conveyor.

According to a preferred embodiment, the invention in its broad aspectcomprises a pair of gage elements that are respectively disposed onopposite sides of a plate to be measured, and an electrical ormechanical differential mechanism operated by both gage elements toprovide an indication of the thickness of the plate therebetween. In amanner to be described, the gage elements are moved to identicalpositions relative to opposite sides of the plate being measured,preferably at points spaced equal distances from the opposite sides ofsuch plate, so that the differential mechanism provides an indication oithe relative distance between the gage elements, and thus an indicationof the thickness of the plate therebetween.

ln a more specic aspect of the invention, the gage elements referred toabove are capacitor terminals of condensers in which the oppositeparallel surfaces of a plate being measured, for example, oppositesurfaces of the flanges or web of a steel beam, re utilized as the othercapacitor terminals thereof. Such condensers are connected respectivelyin tuned self-balancing series-resonant circuits, which are used tocontrol the reversing operation of direct current drive motors thatoperate to move the gage elements or capacitor terminals topredetermined operative measuring positions in which they arerespectively located equal distances from the surfaces of the platebeing measured. When the gage elements are moved to these positions, themotor control circuits which include the series-resonant circuits andthe condensers mentioned above, operate to stop the drive motors and tohold the movable capacitor terminals in their operative measuringpositions. In addition, the drive motors for moving the capacitorterminals are mechanically connected to a differential indicator thatoperates to indicate the relative positions of such terminals and thusthe thickness of the plate o measured. While the differential indicatingmechanism may be either mechanical or electrical, it is preferably asynchro-tie system comprised of a pair of transmitter elementsrespectively coupled to the condenser adjusting drive motors, and adifferential element that is coupled to both of the transmitter elementsand operates to continuously indicate the relative movement imparted tothe transmitter elements by the condenser adjusting drive motors, andthus indicates the relative positions of the movable capacitor terminalsand thereby the thickness of the plate positioned therebetween.

The objects and advantages of the invention will become apparent fromthe following description and the accompartying drawings, which show apreferred embodiment of the invention and modifications of adifferential indicating system that forms a part thereof. in thedrawings:

FIGURE l is a diagrammatic showing oi a preferred embodiment of theinvention that illustrates the manner in which it is operated tocontinuously indicate the thickcss of a plate travelling over a rollerconveyor, the plate in the form of the Iweb of a steel beam; GURE 2 is agraph illustrating the operating charf istics of each of theseries-resonant circuits that form g art of the system shown in FIGUREl, and the manner in which the mechanism shown therein is operatedaccording to the principles of this invention; and

United States iatent 'loe 3,955,415 Patented Nov. 20, 1952 FGURES 3 and4 are respectively diagrammatic views of modified forms of diiferentialindicating apparatus that may be substituted for the differentialindicator shown in FiGURE l.

As shown in FEGURE l the gage of this invention is particularly adaptedto continuously indicate the thickness of a metal plate l formed ofelectrically conductive material in the orm ofthe web ot a steel beamtravelling continuously over conveyor rolls 2. Generally stated, theinvention comprises a pair of gage elements 3 disposed on opposite sidesot the plate l, a pair of reversing drive `rotors fi for driving thegage elements 3` to identical operative measuring positions relative toopposite parallel sides or sur-faces S of the plate 1, in which the gageelements 3' are preferably at points respectively located predetermineddistances from the surfaces S, and a differential indicator, indicatedas a whole by the numeral 6, which is operated by both motors 4 in amanner to be described to indicate the thickness of the metal betweenthe parallel surfaces '5 of the plate i.

The gage elements 3 are respectively mounted for rectilinear movement ina direction normal to the plate surfaces 5 by gear racks 7 that havemeshing engagement with rack pinions S, which are mechanically connectedwith and driven by the drive motors 4 through gear reducing units (notshown). The gage elements 3 further form the movable capacitor terminalsof condensers 9 that form parts of series-resonant circuits ttl whichrespectively control the reversing operation of the motors d accordingto the capacities of the condensers 9 in a manner to be described. Eachof the condenscrs 9 has as one capacitor terminal thereof a gage element3 and, as its other capacitor terminal, one of the parallel platesurfaces of the beam plate l which has a ground connection i1 throughone or more of the conveyor rolls 2. Movement of the gage elements 3toward and away from the surfaces 5 varies the air gaps 12 between thecapacitor terminals 3 and 5 to thereby vary the capacities of thecondensers Si in the series-resonant circuits 10. Change in capacity ofthe condensers 9 by varying the position of the conductor terminals 3and thereby the size of the air gaps l2 is utilized to control theoperation of the drive motors 4 which operate through the pinion 3 andgear racks 7 to move the conductor terminals 3 to predetermined balancedpositions with reference to the plate surfaces 5.

Each of the series-resonant control circuits 10 is energized from a highfrequency source of supply 13 and comprises one of the condensers 9connected in series with an inductor coil le that yforms the primary ofa transformer l5 that has a secondary winding lo. The terminals of thesecondary winding lo are connected to the input terminals of rectiers 17which have their output terminals connected with pairs of conductors i3that respectively form part of control circuits for controlling theoperation of the motors 4l. The control circuit for each motor 4comprises a direct current biasing potentiometer 19 that includes aresistor Ztl and a slide wire contact 2l adjustable to differentpositions along the resistor 2o to vary the direct current biasingpotential delivered through conductor leads 22 to an amplifier 23 thatcontrols the armaturc current supplied to the drive motors 4. Each ofthe drive motors 4 has a held winding 24 that is energized by arectifier 25 connected across A.C. supply buses 26. One of the amplierleads 22 in each motor control circuit is connected with the biasingpotentiometer slide wire 21 and has a normally closed contacter 27therein, and one of the control circuit leads 1S has a normally opencontactor 23 therein. The contactors 27 and 28 are operated by coils 29that are energized by a photoelectric relay comprised of a light source3G and a photoelectric cell 31. When a plate 1 is positioned between thephotoelectric aoeasls relay elements 3l? and 3l, the operating coils 29are energized to open the relay contacts 27 and to close the relaycontacts 2d and thus connect the slide wire contact 2l with the one ofthe amplifier leads 22 through the rectifier i7. Under this condition,the slide wire 2l and rectitier i7 of each motor control circuit areconnected in series opposition to supply a motor control potential tothe amplitier 23 according to the energization of the secondary windingsi6 by the primary windings ld of the series-resonant circuits itl. Thisresults in an operation of the motors 4 that moves the capacitor 3 ofthe condensers 9 respectively to positions relative to the capacitorterminal surfaces 5 that arc determined by the setings of the slide wirecontacts 231. When these positions are reached, the outputs of therectiers It? are balanced against the direct current bias potentialssupplied by the slide wire contacts 2i so that no control current issupplied to the amplifiers 23 which thus interrupt the flow or armaturecurrent to the drive motors 4l. Under this condition, the drive motorsft stop and operate to hold the capacitor terminals 3 in a predeterminedposition relative to the plate surfaces 5.

The manner of operation of the series-resonant circuits l@ and thebiasing potentiometers i9 will be best understood by referring to FIGURE2 which shows the output voltage E plotted against the capacitance C ofthe seriesresontant circuits 1 6. The slide wire potentiometer 2l isadjusted to provide a battery biasing voltage Eb which is less than thepeak output of the control circuits liti. The polarity of the armaturecurrent fed to the motors 4 and their respective direction of rotationis thus dependent on the voltage E as determined by the capacities ofthe condensers 9. The motors 4 will thus operate to drive the movablecapacitor terminals 3 to positions in which the series-resonant circuitoutput voltages E are equal to the direct current biasing voltages Eb.When this balanced i condition is obtained, the relative distancebetween the capacitor terminals 3 of the condensers 9 furnishes anindication of the thickness of the plate fl between its parallelsurfaces 5.

As indicated above, the thickness of the plate l is indicated by adifferential indicator 6. As shown in FIGURE l of the drawings, thedifferential indicator, according to the preferred embodiment of theinvention, is a synchrotie system which comprises a pair of transmitterelements T and a differential element D. The transmitter elements T eachcomprise single phase rotors 35, the windings of which are connectedacross the alternatin y current supply buses 26, and polyphase statorwindings 36. The stator windings 36 have a transformer coupling witheach other through the polyphase stator winding 37 and polyphase rotor`winding s of the dilierential element D. The rotors 35 of thetransmitter' elements T are provided with mechanical connections to thedrive motors 4 through the gears d and a gear reduction drive (notshown). In this manner, the rotors 35 are driven to angular positionswhich correspond to the relative positions of the gage elements orcapacitor terminals 3 relative to the plate surfaces 55, and the rotor38 of the diiferential element D is rotated to a position thatrepresents the angular difference in the positions of the rotors 35 ofthe transmitter elements' T, and this angular difference furnishes anindication of the distance between the capacitor terminals 3 and thusthe thickness of the plate l between its parallel surraces 5. Anindicator 39 is operated by the rotor 38 and is calibrated to furnish anindication of the thickness of the pate 5.

As shown in FEGURE 3 of the drawings, a mechanical differentialmechanism, comprising a differential gear unit may be substituted forthe synchro-tie system shown in FIGURE l. The gear unit i0 comprises apair of bevel gears All which are mechanically connected with the motors4 for rotation thereby, preferably through gear reducing units (notshown). A ditierential gear 42 has meshing engagement with each of thegears di so that its angular position represents the difference betweenthe relative rotation of the gears di and thus furnishes an indicationof the distance between the gage elements 3. The differential bevel gear42 is connected with an indicator 43 which is calibrated to furnish anindication of the thickness of the plate l.

in the modification shown in FIGURE 4, the indication of thickness ofthe plate l is furnished by a voltmeter t5 that has its terminalsconnected with movable slide wires do adjustable along the length ofpotentiometer resistors The slide wires d6 are connected through gearreducing units (not shown), with the drive motors d so that theirrelative positions along the potentiometer resistors 47 furnish anindication of the relative movement of the gage elements 3 by the motors4. The deflection of the voltmeter 45 will thus furnish an indication ofthe distance between the gage elements 3 and thereby an in-v dication ofthe thickness of the plate l between its parallel surfaces 5.

Since the operation of the apparatus of this invention will be apparentfrom the foregoing, it will be suiiicient to indicate that the relaycontactors 27 and 2S are operated to place the motors l under thecontrol of the series-resonant circuits itl whenever a plate 5 ispositioned between the photoelectric relay elements 30 and 3l andthusoperates to interrupt the beam of light from the light source to thephotosensitive element 3l. When the relay contactors Z7 and 28 areoperated in this manner, the motors d rotate in directions that move thegage elements 3 to positions in which the rectified outputs of theseries-resonant circuits lll operate to produce direct currentpotentials that are balanced against the outputs of the direct currentbiasing potentiometers i9. When this balanced condition is obtained, thegage elements 3 are respectively located in positions respectivelyspaced predetermined distances from the opposite plate surfaces 5 of theplate l, and in which the distance between the gage elements 3 thusfurnishes an indication of the thickness of the plate i. This thicknessis indicated by the dilierential indicators 6 as explained above.

While the gage elements 3 are movable capacitor terminals of thecondensers 9 in the preferred embodiment of the invention as explainedabove, it will be understood that the invention is capable ofmodification to a mechanical system in which the gage elements 3 aremoved to positions in contact with the surfaces 5. A modification ofthis character could be provided, for example, by substituting rollercontacts for the gage elements 3 and by providing a spring for biasingthe movement of the gear racks 7 to positions in which such rollercontacts have rolling engagement with the surfaces 5. In such case,inward and outward movement of the gear racks '7 in response to changingthickness of the plate 1 would operate through the gears S to actuatethe differential indicator o and furnish an indication of the thicknessof the plate l.

While one embodiment of my invention has been shown and described itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

I claim:

1. An apparatus for measuring the thickness between parallel surfaces ofa plate formed of electrically con ductive material comprising, thecombination with said plate, of a pair of series-resonant circuitsrespectively including an inductor and a condenser connected in series,each of said condensers comprising one of said plate surfaces as onecapacitor terminal thereof and a second capacitor terminal spaced fromand mounted for movement toward and away from said one capacitorterminal, said second capacitor terminals being disposed on oppositesides of said plate, means including separate motor drives for movingsaid second capacitor terminals relative to said one capacitorterminals, separate motor control means operated by said series-resonantcircuits respectively tor operating said motor drives to move saidsecond capacitor terminals to operative measuring positions locatedpredetermined distances respectively from said one capacitor terminalsand in which the capacities of said condensers have a predeterminedvalue, and differential means actuated by said motor drives forindicating the relative distance between said second capacitor terminalsand thereby the thickness of said plate.

2. An apparatus as defined in claim 1 characterized by said differentialmeans being a differential synchro-tie system comprising a pair oftransmitters respectively having rotor windings connected with saidmotor drives Ifor rotation thereby and stator windings, a differentialreceiver having a stator winding connected with one of said transmitterstator windings and a rotor Winding connected with the other of said'transmitter stator windings, and a plate thickness indicator connectedfor operation by said differential receiver rotor winding.

3. An apparatus as defined in claim 1 characterized by said differentialmeans being a differential gearing comprising a pair of bevel gearsconnected with said motor drives for rotation thereby, a differentialbevel gear in meshing engagement with both of said bevel gears, and aplate thickness indicator connected with said differential bevel gearfor operation thereby.

4. An apparatus as defined in claim 1 characterized by said differentialmeans comprising a pair of potentiometers respectively including aresistor and a slide wire contact adjustable over the length thereof,means connected with said motor drives for moving said slide wirecontacts along the length of said resistors in accordance with themovement imparted by said motor drives to said second capacitorterminals, and a voltmeter connected in series with said slide wirecontacts for indicating the thickness of said plate.

5. An apparatus -for continuously measuring the thickness betweenparallel surfaces of a plate formed of electrically conductive materialcomprising, the combination with said plate, of a pair of condensersrespectively comprising one of said plate surfaces as one capacitorterminal thereof and a second capacitor terminal spaced from and mountedfor movement toward and away from said one capacitor terminal, meansincluding separate motor drives for moving said second capacitorterminals relative to said one capacitor terminals, and separate meanscontrolling the operation of each of said motor drives respectivelycomprising a series-resonant circuit including one of said condensersand an inductor connected in series therewith, a control circuitenergized by said series-resonant circuit including means for producinga direct current potential that varies with the capacity of said onecondenser, and separate means respectively respectively responsive tosaid direct current potentials for operating Said motor drives to movesaid second capacitor terminals to predetermined positions spaced equaldistances from said plate capacitor surfaces, and differential meansactuated by said motor drives for indicating the relative distancebetween said second capacitor terminals and thereby the thickness ofsaid plate.

6. An apparatus as defined in claim 5 characterized by the provision oflmeans responsive to the presence of a plate between said secondcapacitor terminals for rendering said motor drive control meansoperative, and operating to render said motor drive control meansinoperative when said plate moves out of the space between said secondcapacitor terminals.

7. An apparatus as dened in claim 6 characterized further by said plateresponsive means comprising a photo-electric relay.

8. An apparatus as defined in claim 5 characterized' by each of saidmotor drive control means comprising adinstable biasing means connectedin series opposition with said direct current producing means foradjusting the said predetermined position to Which said second'capacitor terminals are moved by their respective motor drives.

References Cited in the tile of this patent UNITED STATES PATENTS2,548,590 Cook Apr. 10, 1951 2,831,254 Phillips et al. Apr. 22, 19582,930,976 Hirdler Mar. 29, 1960 FOREIGN PATENTS 207,792 Australia Dec.14, 1954

